The invention relates to a method for detuning the natural frequency of a rotatable part which is rotatably disposed in the shaft bearing, and in the case of which the axis of rotation of the rotatable part is arranged axially identically with the axis of rotation of the shaft bearing, as well as to a tunable rotatable part which is rotatably disposed in the shaft bearing, and in the case of which the axis of rotation of the rotatable part is arranged axially identically with the axis of rotation the shaft bearing.
In machine construction, rotatable parts are generally rotatably held by means of shaft bearings or pivot bearings, such as ball bearings, tapered-roller bearings, slide bearings, etc. In the case of rotatable part/shaft bearing connections, changes of the clamping conditions, as, for example, a play, may occur. The changes are generally not static but may change, particularly as a result of thermal effects. Various effects are connected with the change of the clamping conditions of the rotatable part in the shaft bearing. Thus, particularly the natural frequencies and/or the vibration amplitudes of the rotatable part will change. Sometimes, a compensation of the occurring changes will be achieved in that the rotatable part/shaft bearing connection is prestressed particularly by a spring or by an elasticity of the material, the prestressing partially affecting bearing shells.
Compensation arrangements of this type are known, for example, from German Patent Documents DE 195 41 245 A1, DE 38 10 448 C2, DE 93 01 334 U1 or DE 31 23 590 A1.
Furthermore, machines having rotating parts have at least usually a certain disturbing sound effect. One reason for these disturbing noises is, among others, that the rotating rotatable parts, particularly shafts, introduce vibrations into other components. Resonance frequencies are important for the transmission of vibrations between components and for the introduction of vibrations from one component to another. The mathematical relationship of this frequency-dependent transmission is called transmission function.
From U.S. Patent Document U.S. Pat. No. 5,332,061 A1, a method is known for suppressing vibrations introduced into the vehicle body as well as a corresponding vehicle. The concerned introduced vibrations originate from the engine and, in this case, particularly from the moving parts, such as the rotating crankshaft or camshaft. The vibrations are transmitted at the connection points of the engine with the vehicle body. For damping these vibrations, the vehicle has shakers, thus, mechanical vibration exciting devices which are arranged in the area of at least some connection points of the engine with the vehicle body. During the operation of the engine, the shakers are excited as a function of the rotational speed of the engine at the resonance frequencies in antiphase to the vibrations coming from the engine, whereby the transmission of the introduced vibrations is at least dampened. In this case, the corresponding frequencies and their amplitudes for the artificial secondary vibrations introduced in a targeted manner are taken from a previously filed data field.
From U.S. Patent Document U.S. Pat. No. 5,434,783 A1, a vehicle is known, in the case of which the sound effect audible inside the occupant compartment is influenced by sound waves. In addition to normal loudspeakers, a piezoelement is also used here which excites the vehicle body at least in areas to carry out vibrations and thereby causes it to emit sound waves; that is, the piezoelement acts like the coil of a loudspeaker while the vehicle body represents the vibrating membrane. By means of the known method and the known system, an improvement of the subjective sensation inside the occupant compartment is achieved.
A further development of the above system for influencing the subjectively perceived driving sensation is known from German Patent Document DE 195 31 402 A1. According to this document, as a function of a parameter and in this case particularly of the rotational engine speed and/or the vehicle speed, not only the airborne sound but also the structure-borne sound or vibrations perceived by the body are influenced. For this purpose, depending on the size of the parameter, certain data are read out of a data field and, by means of vibration exciting devices are converted to artificial vibrations which, among others, can also be perceived by the body. As a result of these measures, in conjunction with the influencing of the acoustically perceived airborne sound, positive as well as negative interferences of the targeted introduced artificial secondary vibrations can be generated with the primary vibrations which occur on the vehicle side when the vehicle is operated. As desired, the interferences can reduce the perceived impression or simulate a certain impression, for example, a shifting in the case of a vehicle provided with an infinitely variable speed transmission.
It is an object of the invention to develop a method by means of which the perceivable vibrations of an engine having rotating rotatable parts and, at the same time, a possibly occurring axial play can be at least reduced. Furthermore, it is an object of the invention to suggest a new system by means of which perceivable vibrations and, at the same time, a possibly occurring axial play can be at least reduced.
According to the invention, as the result of the targeted and reversible change of the axial adjusting unit having particularly piezoelements or of the contact pressure axially acting upon the rotatable part, the axial clamping conditions during the operation can be changed by a targeted intervention from the outside. The changing of the clamping conditions has, for example, the result that the values of the inherent vibrations of the rotatable part and also the transmission function from the rotatable part to another component are changed. As the result of the change of the transmission function, the transmission of vibrations, thus of the transmittable energy, coming from the rotatable part, into another component are changed, particularly at least reduced.
In the case of the axial adjusting unit, the intervention takes place by the application of an electric voltage. This measure leads to a change of the resonance or natural frequencies of the rotatable part and also to a change during the transmission and introduction of vibrations. The respective resonance frequencies are important for the transmission of vibrations between components and for the introduction of vibrations from one component to another component, The mathematical relationship of this frequency-dependent energy transmission or vibration transmission is called transmission function.
As the result of this intervention, the resonance between the rotatable part and the environment transmitting the vibrations is therefore disturbed, whereby the sound effects which are particularly perceived to be disturbing are reduced. Since, in the case of an existing axial play, the change of the axial clamping conditions is connected by an axial movement at least of a part of the axial adjusting unit, simultaneously at least a reduction of this axial play can be achieved.
In a preferred manner, this is expedient in the case of a crankshaft and/or camshaft of an internal-combustion engine, preferably a diesel engine or gasoline engine, as a rotatable part because, in a simple fashion, the introduced vibrations and of these particularly the sound emission inside an occupant compartment of a combustion-engine-driven vehicle can be influenced.
This method and this arrangement can expediently be used in the case of rotatable parts of electric motors, as particularly rotors, but also in airplane engines, for example, jet engines or propellers.
In a preferred manner, the use of the invention is also expedient in the case of a crankshaft and/or camshaft of an internal-combustion engine, preferably a diesel engine or gasoline engine, as a rotatable part because, in a simple fashion, the introduced vibrations and of these particularly the sound emission inside an occupant compartment of a combustion-engine-driven vehicle can be influenced. The influencing of the noise level, which the operator of a vehicle perceives, in particular, as disturbing and which comes at least partially from the engine, takes place at the site where it arises and not, as previously customary, only at the site where the operator perceives it. In an advantageous manner, this reduces, among other things, the expenditures with respect to the electronic control system and the equipment construction (microphone, loudspeaker and the like).
Meaningful further developments of the invention are contained in the subclaims. In addition, the invention is explained in detail by means of embodiments illustrated in the drawings.